Method of and apparatus for testing the hearing



F. w. KRANZ METHOD OF AND APPARATUS FOR TESTING THE HEARING Dec. 28 1926.

Original Filed Nov. 20. 1922 .ATE

f'n ederz'ck v Kmn Reissued Dec. 28, 1926.

' UNITED STATES -Re.- l6,512

PATENT OFFICE.

FREDERICK W. KRANZ, OF GENEVA, ILLINOIS.

METHOD OF AND APPARATUS FOR TESTING THE HEARING.

Original No. 1,528,714, dated Harp 10, 1925, Serial No. 602,021, filed November 20, 1922. Application to! reissue filed .Tune 19, 1925. Serial No. 38,374.

In testing the hearing, difiiculty has been experienced heretofore in obtaining a reproducible standard of sound, so that the subject wh'osehearing has been tested by one apparatus might give a decidedly differentresult when tested by another apparatus, or even when tested by the same apparatus at another time. Another cause of inaccuracy in such tests heretofore has been that there is no certain and dependable relation between the various adjustments of the apparatus and the loudness of the sound produced. Also there has been di-fliculty in ascertaining the relation between the adjustments and the loudness at different pitches.

It is an object of the present invention to provide an apparatus which shall yield a sound whose loudness can be' accurately determined from the adjustments of the apparatus.

It is a further object of this invention to provide such an ap aratus which can be'accurately reproduced It is a further object of this invention to produce a sound-producing apparatus in which the relation between the sound energy and the adjustments of the apparatus may be certainly known for sounds of various pitches.

It is a further object of this invention to tion between the pitch and the sensitiveness' of the subject to sound.

It is a further object of this invention to provide a method by which the presence of such irregularities maybe certainly and uickly found with a minimum of labor on t e part of the investigator and a minimum of. fatigue or other inconvenience on the part of the subject.

Other and further important objects ofthednvention will be apparent from the dis- As shown on the drawings:

It is a further object of this invention to closures in the accompanying drawings and the following, specification.

The invention (in a. preferred form) is illustrated'on the drawings and hereinafter more fully described.

On the drawings: V

Figure l is a diagram of a circuit showing one form of my invention.

Figures 2 and 3 are schematic sectional drawings illustrating the sound instrument used in this circuit.

Figure 4 is a diagram of a portion of "a circuit showing a modification.

The circuit includes a source of alternating current. I prefer to use for this purpose a generator set such as is frequently used in producing 7 connection with radio work. It comprises an 'audion 10 connected in a way which is wellunderstood workers in the art, with an adjustable con enser 11 and an adjustable inductance 12. The output of this generator is connected'to an amplifier which-includes an audion 13. The connections 'may includev a key or other interrupter 14 for the purpose of controlling the stopping and starting of the action. V

The output circuit of the'amplifier is inductively connected as shown at 15 to a circuit which includes a succession of inductances 16 in series and a succession of condensers 17 in shunt; Such arrangements,as is well understood by workers in the electrical art," will, when properly chosen, readily transmit a current of the fundamental frequency delivered by the amplifier but will shunt out harmonics or other higher frequency currents. For this reason, this portion .of the circuit is spoken of an as electrical filter.

The output side of the filter is connected to a. portion of the circuit includinga succession of resistances 18 in series and 19 in shunt. As shownon the drawing, only'one resistance 19 across the line is shown,.but it is ,understood that any number that is desired may be used. Some or-all of the resistances 18 may be adjustable and the resistancesl9 likewise may be adjustable. If

desired, the adjustment may extend to the complete elimination of some of the units consisting of a resistance 18 in each line and a resistance 19 across the lines. Also known resistances may be added either in series or "been-selected because it is possible to computein dynes'per square centimeter the presin parallel whendesired. when; the series resistances are changed, it isnecessary to keep the resistance of the two sidesof the line ofnearly equal resistance to ensure proper balancing. It is the function of this part of the circuit to regulate the intensity of thev electrical oscillations arriving at the sound producing instrument. It does this by causing a predetermined diminution in the energy and is consequently called the attenuator. 'The resistances therein are adjusted until the desired degree of attenuation is secured. .A very convenient arrangemenhbut one which is not essential to the invention, is

to have these resistances arranged in sets, each set corresponding to a definite percentage of attenuation. The several sets can then be so connected that each is putinto or removed from the circuit by the movement of a sinlgle switch handle.

rom the inductive connection up to this point in the circuit, the arrangement is i symmetrical, each inductance .16 being matched-byan equal inductance 16 in the other line, and the capacities. 17 being connected between the mductances. In the same way, "each resistance 18 is matched by a like resistance 18 in the other line and 1 I the shuntslQ are connected between the resistances 18." .j

ere'ls introduced into one line an arrangement for 'fmasuring the current.

l-referably a non-inductive arrangement is used,"and a resistance 21 is placed in the other line to balance this non-inductive resistanc. Thec'u'rrentmeasuring instrument chosen consists *of a heating element shown at 20, which acts to heat the junctions of a thermocouple 22 ,which is connected to a delicate galvanomet'er "or microammeter 23.

Either in place of the key 14'or in addition to it, a switch '60 may be inserted just .in' frontof the sound producing device. In

order to. keep-the circuit symmetrical, a double poleswitch is used.

.At- 24 there is shown connected across-the line an instrument for producing. sound fromthe electrical oscillations. The instrument which I have chosen for this purpose and which .is'known as a thermo-phone has surechangeg produced by this instrument whenthe ene of the electric current dewn. From values thus obtained, thes energy may be calculated.

Thai-relations ween the two depend on o' f the instrument which may be I from its physical characteristics and-sq ma be predicted with certainty. phone consists of a strip of platinum2 51fjwhichis very thin. Preferably itsfthickness does not exceed .0002 centimeter,. This .strip is mounted, in brass clamps '26 to which the wires 27 are con-,

the form of a telephone receiver.

' the air in the chamber.

' nected. The strip 25 is enclosed in a chamber. This chamber may convenientl take urrent throughthe strip 25 heats it and so heats The temperature andso the pressure of this air therefore changes with changes in the current. When the instrument is held to the ear, these pressure changes are communicated to the ear-' drum through the open side of the chamber.

The pressure withinthe chamber being a function of the. temperature, the pressure changes may, be accurately computed from I the measurements of the current. As the heat produced is proportional to the s uare of the current, the heat changes wil be larger and follow the current changes more faithfully if the alternating current 1s superposed on a direct current. This direct current is supplied by a battery'31 and measured by an ammeter 32." The alternating current from the transformer 15 is prevented from reaching the battery and am meter by inductances 33, and the constant current from the battery 31 is prevented from reaching the microammeter 23 by careceiveris to be used, the circuit is modified as illustrated in Figure-i in which the inductances 16 and the capacity 17 farthest from the transformer 15 are shown at the left of Figure 4. Adjustable resistances 38.

in series in each side of the line and adjustable resistances 39 across the line, corresponding respectively to the resistance 18 and 19 are provided in this modification, but they are preferably placed upon the other side of the measuring instrument 20 and its balancing resistance 21, because the current used through a telephone receiver is so small compared with that used through a thermo-phone that difiiculty would be experieneedin measuring it directly. The micro-j ammeter 23, placed in-the situation shown in Figure: 4, measures a current which is very large compared with the current flowing through the telephone receiver, but the ratio between the two is easily computed from the resistances. I

To facilitate the calculation of the amount by which the electrical current is .attenuated by the resistances 38 and' 39, it is important that the part of the circuit beyond the last shunt 39 should, have a constant resistance. The impedance of a telephone .re-

.circuit acts as an attenuator.

ceiver is not pure resistance and moreover this impedance varies with the frequency.. --There fore thetelephone receiver is shunted by a small resistance 41. This small resistance 41 is in series with larger resistances of such magnitudes as to bring the whole resistance of the circuit up to the value wished. Thus the impedance of the telephone receiver has only a small effect on the circuit as a whole, and this latter has prac.-. tically a constant resistance.

In an exemplification of this circuit which ll have found useful, each of the resistances 40 was about 97 ohms, while the resistance 41 was 6 ohms, which gave to the combination of resistances 40, hand telephone receiver 42 a substantially constant resistance at all frequencies of approximately 200 ohms.

In the operation of the device, in the circuit'shown in Figure 1, the generator and amplifier set up oscillatory electrical currents in the transformer 15. The frequency .of these oscillations is adjusted in lar e steps by turningl the dial of the adjustab e capacity 11. T e finer adjustments of the frequency are effected by. means ofthe adjustable inductance 12. The electrical filter made up of properly chosen inductances 16 and capacities 17 separates from the output of the transformer 15 all frequencies except the fundamental. Seriesresistances 18 and the. shunt resistances 19 cause a dissipation of part of the energy of the electrical oscillation or in other words this part ofthe These resistances are adjusted until the reading of the microammeter 23 shows that the input into the thermo-phone is of the desired size. The

current fromthe battery 31 is determined by'the ammeter 32 and the temperature of the platinum strip 25 is thus obtained;

From the reading of the microammeter 23 and the. ammeter 32, therefore, the pressure *changesproduced by thethermo-phone may be determined.

The apparatus may beused byleaving the frequency adjustments at 11 and 12 con-. stant, varying tie adjustments at Hand- 19 for intensity changes until the limit-of audiliility for the particular frequency is found The adjustmentsat 11 and 12 may then be changed to elect a different frequency and the exploration by means of the adjustments at 18 and 19 repeated.

While the apparatus described is available for this method, a better method is as follows: The operator adjusts the capacity 11 so that the range of frequencies which he wishes to investigate may be produced by changes inthe inductance 12. He then requests the subject who is listening to the sounds from the 't hermo-phone 24 or telephone receiver 42 to vary the frequency back forth over thi si v-ffqfi means of the handle controlling-the1nduc.' I

tance 12. The operator adjusts the. resist-Q ances 18 and 19 so as to give ad'efinite soundenergy output, and the subject, by means of 1115 control of the inductance 12, deter;

mines overwhat portions of the frequency" I range, if any, the sound 'is audible. noting the adjustment of the indicator on the inductance, the operator can determine: the frequencies of the audible portions of.

the frequency range and from the readings of the mi'cro-ammeter and. also of the resistances 18 and 19 in the case of the useof the telephone receiver,.he can determine the intensity of the sound. The operatorthen adjusts the resistances 18 and 19 so as to change the sound intensit known amount and the sub ect again determines what portions of the frequency range are audible, and readings are again taken to determine the frequencies and intensities ofthese ort-ions, and so on. A preferred method of procedure is to have the first ad-\ justmentIof-the resistances 18: and 19 such that the sound intensity is not sufficient to be audible to the subject at any point in the frequency range, and succeeding adjustments of the resistances to be such that theintensity is increased in regular steps until all of the frequency range is audible, ob-

by a. definite servations being made by the subject after each change of intensity. By noticin whether or'not he can detect a stopping and starting of the sound corresponding tothe opening and closing of the switch 60 (or key 14),"the subject canmake a test as to whether a given intensity is beyond the limits of audibility. Sometimes a subject displays marked and abrupt changes in sensibility to soundswith changes of pitch and this method of testing is much more adapt ed tothe discovery and exploration of these irregularities than a method dependent on changes of intensity using a series of constant pitches.

When the subject is a very. deaf person or when the sounds being investigated are of such low pitch orof such high pitch as to be very near the pitch limit of 'audibility,

the arrangement shownin Figure 4 is used instead of that shown in Figure l. The

rocedure, however, is the same except that instead of the reading of the microammeter 23 giving directly the input into the sound producing 1nstrument I a fraction only of' the current shown by the microammeter 23 reaches the telephone receiver 42 this fraction being calculable from the values of the resistances 18 and 19. The telephone receiver itself,'as already explained, must be calibrated by comparision with .a thermo-.

phone." I v I am aware thatnumerous'details, both of the apparatus and of the method, may

be varied through a wide range without departing from the spirit of this invent1on,.

mined ratio to the energy imparte to said device, means for imparting energy to said sound producing device, and means for measuring the energy thus imparted.

2. In a sound producing device, a generatorof electrical alternating current, means for measuring the energy of said alternating current, and means for transforming theenergy of the electrical alternating current into sound energy, the latter means having a known transformation ratio..

3. In a device of the class described, means for generating electrical alternating currents, means for adjusting. the frequency of said alternating currents, means for amphfying said alternating currents, connections between the two including means for starting and stopping the operation, means for separating from the amplified alternating currents all alternating currents of a fre quency different from that for which adjustment is made, adjustable means for attenuating the electrical alternating current, means for measuring theenergy of the attenuated alternating current, and means for transforming said alternating current into sound energy.

I 4. In-combination, a generator of electrical alternating current, an electrical filter, an attenuating circuit, means for producing sound from electrical alternating current, and a device for measuring the electrical energy of said alternating current.

. 5. In an apparatus for investigating hearing, a generator of electrical alternating currents including an electrical oscillating C1I'- cuit, variable reactance in the oscillating circuit whereby the frequency of the generated current may be gradually varied'over a considerable range, means for transforming the electrical energy into sound energy and means disposed between said first means and said generator for adjustably varying the intensity of the electrical energy passing into said first means.

6'. In an apparatus for investigating hearing, a generator of electrical alternating currents, including an electrical oscillating circuit, variable inductance in the oscillating circuit whereby the frequency of the generated current may be gradually variedover a considerable range, means for transforming the electrical energy into sound energy and means controlling the current into said first means for adjustably varying the intensity of said sound energy.

7. The method of investigating the intensity limits of audition which consists in electricallyproducing a sound of known intensity, making electrical adjustments to cause the pitch of said sound to be altered until the same is inaudible to the listener, noting the ,frequency and intensity at the limits thus found, altering by a predetermined degree the intensity of sound produced, and causing the pitch to be again altered as before, and so on. v

8. In an apparatus for investigating hearing, a generator of electrical alternating currents including an electrical'oscillating circuit, variable reaciance in the oscillating circuit whereby the frequency of the generator current may be gradually varied over a con-' siderable range, means for transforming the electrical energy into sound energy, and means for adjustably varying the intensity of said sound ener I c 9. A method of investigating the intensity limits of audition which consists in electrically producing sound of definite intensity, effecting inductive variances to determine the frequency range of audibility, noting the frequencies within the limits of audition, determining the intensity of sound corresponding to the audible frequencies noted, and altering the intensity of sound by a predetermined amount, and so on.

10. A method of investigating the intensity limits of audition which consists in electrically producing sound of known intensity, determining the frequency range ofaudibility, noting the frequency ranges at which the sound is audible, and determining the intensity of the sound which is audible within the investigated range.

In testimony whereof, hav 'h t subscribed by name. 1

FREDERICK W. KRANZ. 

